1. Field of the Invention
The present invention generally relates to high-pressure pumps for pumping incompressible fluids. More particularly, the present invention relates to the fluid-handling sections, or fluid ends, of such high-pressure fluid pumps.
2. Summary of the Prior Art
High-pressure, reciprocating, fluid pumps have been used for many years. Such pumps are employed to pressurize incompressible fluids to pressures upwards of 10,000 pounds per square inch (p.s.i.). A primary use of such pumps is in pumping drilling fluid, or mud, downhole during the drilling of oil wells. Such pumps also are used to provide pressurized fluid for applications such as water-blasting.
Because of the cyclic pressures (atmospheric to 10,000 p.s.i. and upward), and the frequently abrasive process fluid, the operating environment of such high-pressure pumps is very demanding. Therefore, much effort has been dedicated to designing a strong, durable, and easily maintained high-pressure, reciprocating, fluid pump. The high cyclical pressures encountered in such pumps makes pump components susceptible to fatigue failure. The presence of the process fluid, itself often corrosive, increases the susceptibility of pump components to fatigue failure through wet and corrosive fatigue. Many pump designs require crossbores, which intersect the pump cylinder, to deliver and carry away the process fluid. These intersecting crossbores create stress-concentrations, further rendering the pump susceptible to fatigue failure, and limiting the maximum pump pressure. Many known pumps require extremely high-strength materials to avoid the problem of fatigue failure. U.S. Pat. No. 3,260,217, Jul. 12, 1966, to Thresher, discloses a typical pump fluid end having intersecting crossbores.
Due to the abrasive nature of many of the process fluids (even tap water has a surprising amount of abrasive material suspended in it) abrasive wear of the valves and other components of the pump can be a significant problem. Most known pump designs use carefully machined and toleranced metal-to-metal suction and discharge valves. U.S. Pat. No. 5,037,276, Aug. 6, 1991, to Tremoulet, Jr., and U.S. Pat. No. 4,878,815, Nov. 5, 1989, to Stachowiak, are typical of such pumps having metal-to-metal valve assemblies. Such precision valves are expensive to manufacture and can be very difficult to replace in the field.
Because of high pump pressures, leakage from such pumps becomes a problem. Some known pumps use the pressure of the process fluid to hydrostatically bias the valve assembly in engagement with the cylinder. These pumps require extremely heavy discharge manifolds to contain the high pressure encountered. See U.S. Pat. No. 4,878,815, Nov. 7, 1989, to Stachowiak, for example. The weight and bulk of these discharge manifolds requires more than one person to remove the manifold for repair of the pump.
Cavitation, caused by gas entrapped in the pump fluid, can cause vibration and be very destructive to the pump. Therefore, such pumps must be designed to purge entrapped gas from the pressure chamber of the pump to minimize cavitation and the resulting destructive vibration.
It is, therefore, desirable to have a high-pressure, reciprocating, fluid pump that is strong, durable, easily and quickly repaired in the field, capable of pumping abrasive fluids, and easy and inexpensive to manufacture.